In rotary air valves such as used in vehicle air conditioning, heating and ventilating systems, the periphery of the rotary air valve is required to seal against the surrounding case in a consistent manner with a minimum of effort. However, the peripheral sealing surface of a rotary air valve normally has sliding contact as compared with the face-to-face contact of a flapper valve making it difficult to control the contact pressure between the seal surfaces and with a minimum of friction. Typically, seal materials are selected, such as plastic foam, felt, wool pile, and rubber, in combination with various retainers in an attempt to control the contact pressure between the seal surfaces. However, the complexity of such combination designs requires added space, is costly and gives inconsistent sealing and frictional characteristics at various climatic conditions. For example, the different expansion characteristics between the valve, case and seals at temperature extremes causes inconsistent seal performance particularly at certain low temperature situations where it is possible for the valve to freeze in position. The functional problem of the rotary valve in turn cause high control lever efforts and potential overload of the valve's operating mechanism.